In germany we called that an "Eimer", meaning bucket, when i was around that age. Essentially yeah its sort of a gravity bong. The appeal is that you can macguyver one as a teen without reliable access to smoking accessories.

Take any bucket, or bucket like container, fill it with water. Cut the bottom out of a plastic bottle, take some aluminum foil to mold a heat resistant headpiece/sieve for the bottle. Prepare your smoke and fill it in the headpiece, sink the bottle until a few centimeters still stick out, put the headpiece on and light it up while slowly and steadily raising the bottle until only a few centimeters are below water. Take off the mouthpiece and proceed with the picture, basically force loading your lungs while you lower the bottle again.

A lot of bang for your buck and you can dispose of it easily.